Cleanup and guard tuple's constructor SFINAE. Fixes PR22806 and PR23256.
There are two main fixes in this patch.
First the constructor SFINAE was changed so that it's evaluated in two stages
where the first stage evaluates the "safe" SFINAE conditions and the second
evaluates the "dangerous" ones. The key is that the second stage is lazily
evaluated only if the first stage passes. This helps fix PR23256
(https://llvm.org/bugs/show_bug.cgi?id=23256).
The second fix is for PR22806 and LWG issue 2549. This fix applies
the suggested resolution to the LWG issue in order to prevent the construction
of dangling references. The SFINAE for this check is contained within
the _PreferTupleLikeConstructor alias template. The tuple-like constructors
are disabled whenever that trait returns false.
(https://llvm.org/bugs/show_bug.cgi?id=22806)
(http://cplusplus.github.io/LWG/lwg-active.html#2549)
llvm-svn: 266461
diff --git a/libcxx/include/tuple b/libcxx/include/tuple
index a39eeda..6a65aba 100644
--- a/libcxx/include/tuple
+++ b/libcxx/include/tuple
@@ -502,6 +502,28 @@
}
};
+template <bool _IsTuple, class _SizeTrait, size_t _Expected>
+struct __tuple_like_with_size_imp : false_type {};
+
+template <class _SizeTrait, size_t _Expected>
+struct __tuple_like_with_size_imp<true, _SizeTrait, _Expected>
+ : integral_constant<bool, _SizeTrait::value == _Expected> {};
+
+template <class _Tuple, size_t _ExpectedSize,
+ class _RawTuple = typename __uncvref<_Tuple>::type>
+using __tuple_like_with_size = __tuple_like_with_size_imp<
+ __tuple_like<_RawTuple>::value,
+ tuple_size<_RawTuple>, _ExpectedSize
+ >;
+
+
+struct _LIBCPP_TYPE_VIS __check_tuple_constructor_fail {
+ template <class ...>
+ static constexpr bool __enable_explicit() { return false; }
+ template <class ...>
+ static constexpr bool __enable_implicit() { return false; }
+};
+
template <class ..._Tp>
class _LIBCPP_TYPE_VIS_ONLY tuple
{
@@ -509,6 +531,118 @@
base base_;
+ template <class ..._Args>
+ struct _PackExpandsToThisTuple : false_type {};
+
+ template <class _Arg>
+ struct _PackExpandsToThisTuple<_Arg>
+ : is_same<typename __uncvref<_Arg>::type, tuple> {};
+
+ template <bool _MaybeEnable, class _Dummy = void>
+ struct _CheckArgsConstructor : __check_tuple_constructor_fail {};
+
+ template <class _Dummy>
+ struct _CheckArgsConstructor<true, _Dummy>
+ {
+ template <class ..._Args>
+ static constexpr bool __enable_explicit() {
+ return
+ __tuple_constructible<
+ tuple<_Args...>,
+ typename __make_tuple_types<tuple,
+ sizeof...(_Args) < sizeof...(_Tp) ?
+ sizeof...(_Args) :
+ sizeof...(_Tp)>::type
+ >::value &&
+ !__tuple_convertible<
+ tuple<_Args...>,
+ typename __make_tuple_types<tuple,
+ sizeof...(_Args) < sizeof...(_Tp) ?
+ sizeof...(_Args) :
+ sizeof...(_Tp)>::type
+ >::value &&
+ __all_default_constructible<
+ typename __make_tuple_types<tuple, sizeof...(_Tp),
+ sizeof...(_Args) < sizeof...(_Tp) ?
+ sizeof...(_Args) :
+ sizeof...(_Tp)>::type
+ >::value;
+ }
+
+ template <class ..._Args>
+ static constexpr bool __enable_implicit() {
+ return
+ __tuple_convertible<
+ tuple<_Args...>,
+ typename __make_tuple_types<tuple,
+ sizeof...(_Args) < sizeof...(_Tp) ?
+ sizeof...(_Args) :
+ sizeof...(_Tp)>::type
+ >::value &&
+ __all_default_constructible<
+ typename __make_tuple_types<tuple, sizeof...(_Tp),
+ sizeof...(_Args) < sizeof...(_Tp) ?
+ sizeof...(_Args) :
+ sizeof...(_Tp)>::type
+ >::value;
+ }
+ };
+
+ template <bool _MaybeEnable,
+ bool = sizeof...(_Tp) == 1,
+ class _Dummy = void>
+ struct _CheckTupleLikeConstructor : __check_tuple_constructor_fail {};
+
+ template <class _Dummy>
+ struct _CheckTupleLikeConstructor<true, false, _Dummy>
+ {
+ template <class _Tuple>
+ static constexpr bool __enable_implicit() {
+ return __tuple_convertible<_Tuple, tuple>::value;
+ }
+
+ template <class _Tuple>
+ static constexpr bool __enable_explicit() {
+ return __tuple_constructible<_Tuple, tuple>::value
+ && !__tuple_convertible<_Tuple, tuple>::value;
+ }
+ };
+
+ template <class _Dummy>
+ struct _CheckTupleLikeConstructor<true, true, _Dummy>
+ {
+ // This trait is used to disable the tuple-like constructor when
+ // the UTypes... constructor should be selected instead.
+ // See LWG issue #2549.
+ template <class _Tuple>
+ using _PreferTupleLikeConstructor = __lazy_or<
+ // Don't attempt the two checks below if the tuple we are given
+ // has the same type as this tuple.
+ is_same<typename __uncvref<_Tuple>::type, tuple>,
+ __lazy_and<
+ __lazy_not<is_constructible<_Tp..., _Tuple>>,
+ __lazy_not<is_convertible<_Tuple, _Tp...>>
+ >
+ >;
+
+ template <class _Tuple>
+ static constexpr bool __enable_implicit() {
+ return __lazy_and<
+ __tuple_convertible<_Tuple, tuple>,
+ _PreferTupleLikeConstructor<_Tuple>
+ >::value;
+ }
+
+ template <class _Tuple>
+ static constexpr bool __enable_explicit() {
+ return __lazy_and<
+ __tuple_constructible<_Tuple, tuple>,
+ _PreferTupleLikeConstructor<_Tuple>,
+ __lazy_not<__tuple_convertible<_Tuple, tuple>>
+ >::value;
+ }
+ };
+
template <size_t _Jp, class ..._Up> friend _LIBCPP_CONSTEXPR_AFTER_CXX11
typename tuple_element<_Jp, tuple<_Up...> >::type& get(tuple<_Up...>&) _NOEXCEPT;
template <size_t _Jp, class ..._Up> friend _LIBCPP_CONSTEXPR_AFTER_CXX11
@@ -562,21 +696,10 @@
template <class ..._Up,
typename enable_if
<
- sizeof...(_Up) <= sizeof...(_Tp) &&
- __tuple_convertible
- <
- tuple<_Up...>,
- typename __make_tuple_types<tuple,
- sizeof...(_Up) < sizeof...(_Tp) ?
- sizeof...(_Up) :
- sizeof...(_Tp)>::type
- >::value &&
- __all_default_constructible<
- typename __make_tuple_types<tuple, sizeof...(_Tp),
- sizeof...(_Up) < sizeof...(_Tp) ?
- sizeof...(_Up) :
- sizeof...(_Tp)>::type
- >::value,
+ _CheckArgsConstructor<
+ sizeof...(_Up) <= sizeof...(_Tp)
+ && !_PackExpandsToThisTuple<_Up...>::value
+ >::template __enable_implicit<_Up...>(),
bool
>::type = false
>
@@ -600,31 +723,12 @@
template <class ..._Up,
typename enable_if
<
- sizeof...(_Up) <= sizeof...(_Tp) &&
- __tuple_constructible
- <
- tuple<_Up...>,
- typename __make_tuple_types<tuple,
- sizeof...(_Up) < sizeof...(_Tp) ?
- sizeof...(_Up) :
- sizeof...(_Tp)>::type
- >::value &&
- !__tuple_convertible
- <
- tuple<_Up...>,
- typename __make_tuple_types<tuple,
- sizeof...(_Up) < sizeof...(_Tp) ?
- sizeof...(_Up) :
- sizeof...(_Tp)>::type
- >::value &&
- __all_default_constructible<
- typename __make_tuple_types<tuple, sizeof...(_Tp),
- sizeof...(_Up) < sizeof...(_Tp) ?
- sizeof...(_Up) :
- sizeof...(_Tp)>::type
- >::value,
+ _CheckArgsConstructor<
+ sizeof...(_Up) <= sizeof...(_Tp)
+ && !_PackExpandsToThisTuple<_Up...>::value
+ >::template __enable_explicit<_Up...>(),
bool
- >::type =false
+ >::type = false
>
_LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
explicit
@@ -647,8 +751,10 @@
template <class _Alloc, class ..._Up,
class = typename enable_if
<
- sizeof...(_Up) == sizeof...(_Tp) &&
- __tuple_convertible<tuple<_Up...>, tuple>::value
+ _CheckArgsConstructor<
+ sizeof...(_Up) == sizeof...(_Tp) &&
+ !_PackExpandsToThisTuple<_Up...>::value
+ >::template __enable_implicit<_Up...>()
>::type
>
_LIBCPP_INLINE_VISIBILITY
@@ -663,7 +769,10 @@
template <class _Tuple,
typename enable_if
<
- __tuple_convertible<_Tuple, tuple>::value,
+ _CheckTupleLikeConstructor<
+ __tuple_like_with_size<_Tuple, sizeof...(_Tp)>::value
+ && !_PackExpandsToThisTuple<_Tuple>::value
+ >::template __enable_implicit<_Tuple>(),
bool
>::type = false
>
@@ -674,8 +783,10 @@
template <class _Tuple,
typename enable_if
<
- __tuple_constructible<_Tuple, tuple>::value &&
- !__tuple_convertible<_Tuple, tuple>::value,
+ _CheckTupleLikeConstructor<
+ __tuple_like_with_size<_Tuple, sizeof...(_Tp)>::value
+ && !_PackExpandsToThisTuple<_Tuple>::value
+ >::template __enable_explicit<_Tuple>(),
bool
>::type = false
>
@@ -687,7 +798,9 @@
template <class _Alloc, class _Tuple,
class = typename enable_if
<
- __tuple_convertible<_Tuple, tuple>::value
+ _CheckTupleLikeConstructor<
+ __tuple_like_with_size<_Tuple, sizeof...(_Tp)>::value
+ >::template __enable_implicit<_Tuple>()
>::type
>
_LIBCPP_INLINE_VISIBILITY